BC Cygni

BC Cygni (BC Cyg, HIP 100404, BD + 37 3903) is a red supergiant and pulsating variable star of spectral type M3.5Ia in the constellation Cygnus.

BC Cygni
BC Cygni is visible as a red star (circled). The bright star at the centre is γ Cygni and north is to the right.
Credit: Erik Larsen
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension  20h 21m 38.55s
Declination 37° 31′ 58.9″
Apparent magnitude (V) 9.0 - 10.8[1]
Characteristics
Spectral type M3.5 Ia[2] (M2 - M5[3])
B−V color index +3.13 - +3.21[3]
Variable type SRc[2]
Astrometry
Radial velocity (Rv)–22.85[4] km/s
Proper motion (μ) RA: –3.856[4] mas/yr
Dec.: –5.835[4] mas/yr
Parallax (π)0.7517 ± 0.1009[4] mas
Distance1,710[5] pc
Absolute magnitude (MV)−7.71[6]
Details[3]
Mass19 M☉
Radius820[7] R☉
Luminosity95,500[7] - 204,000[5] L☉
Temperature3,605[7] K
Minimum (1900)
Radius1,553 R☉
Luminosity145,000 L☉
Temperature2,858 K
Maximum (2000)
Radius856 R☉
Luminosity112,000 L☉
Temperature3,614 K
Other designations
BC Cyg, HIP 100404, HV 3339, BD+37°3903, IRAS 20197+3722, 2MASS J20213855+3731589
Database references
SIMBADdata

It is considered a member of the stellar Cygnus OB1 association, and within it the open cluster Berkeley 87.2 which would place at a distance of 1,500 parsecs (4,890 light-years) of the Solar System; however, according to the measure of the parallax by the satellite Hipparcos (1.20 milliarcseconds). It is less than a degree north of another variable red supergiant, BI Cygni.

BC Cygni was calculated to have an effective temperature of 2,858 to 3,614 K and to vary between 112,000 to 145,000 L☉. The size at its brightest and coolest has been calculated to be 1,553 R☉ compared to 856 R☉ at the hottest and faintest. It is one of largest stars known. If it were in the place of the Sun, its photosphere would engulf the orbit of Jupiter assuming the maximum radius of 1,553 R☉. With a mass of about 19 M☉, it is estimated that the stellar mass loss, as dust, as the atomic and molecular gas could not be evaluators is 3.2×10−9 M☉ per year.[8]

The brightness of BC Cyg varies from visual magnitude +9.0 and +10.8 with a period of 720 ± 40 days.[1] Between 1,900 and 2,000 appears to have increased its average brightness of 0.5 magnitudes.[3]

See also

References
  1. Kiss, L. L.; Szabó, Gy. M.; Bedding, T. R. (2006). "Variability in red supergiant stars: Pulsations, long secondary periods and convection noise". Monthly Notices of the Royal Astronomical Society. 372 (4): 1721. arXiv:astro-ph/0608438. Bibcode:2006MNRAS.372.1721K. doi:10.1111/j.1365-2966.2006.10973.x.
  2. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  3. Turner, David G.; Rohanizadegan, Mina; Berdnikov, Leonid N.; Pastukhova, Elena N. (2006). "The Long-Term Behavior of the Semiregular M Supergiant Variable BC Cygni". The Publications of the Astronomical Society of the Pacific. 118 (849): 1533. Bibcode:2006PASP..118.1533T. doi:10.1086/508905.
  4. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  5. Davies, Ben; Beasor, Emma R. (March 2020). "The `red supergiant problem': the upper luminosity boundary of Type II supernova progenitors". MNRAS. 493 (1): 468–476. arXiv:2001.06020. Bibcode:2020MNRAS.493..468D. doi:10.1093/mnras/staa174.
  6. Levesque, Emily M.; Massey, Philip; Olsen, K. A. G.; Plez, Bertrand; Josselin, Eric; Maeder, Andre; Meynet, Georges (2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought". The Astrophysical Journal. 628 (2): 973. arXiv:astro-ph/0504337. Bibcode:2005ApJ...628..973L. doi:10.1086/430901.
  7. Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal. 158 (1): 20. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd.
  8. Josselin, E.; Plez, B. (2007). "Atmospheric dynamics and the mass loss process in red supergiant stars". Astronomy and Astrophysics. 469 (2): 671. arXiv:0705.0266. Bibcode:2007A&A...469..671J. doi:10.1051/0004-6361:20066353.
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